W—Cu based composite sintered alloys consisting of tungsten particles and a copper matrix are used as materials for high voltage contact points and electrodes since they have a combination of characteristics such as low thermal expansion coefficient of tungsten, high arc resistance and electric conductivity. In particular, a W—Cu based alloy containing 5˜20 wt % of Cu is used as a heat sink material since it has suitable thermal conductivity and the thermal expansion coefficient of W—Cu alloy is similar to that of the ceramics. Moreover, a W—Cu based alloy containing 20˜40 wt % of Cu is used in the manufacture of electric contact materials and electrodes, and shaped charge liner with high density for munitions.
The W—Cu based sintered alloy of this type is mainly produced by sintering of a powder. However, it is not so easy to produce a uniform alloy of high density by sintering in liquid phase or by way of an infiltration method since there is no mutual solid solubility and large difference in specific gravity. Accordingly, by adding a small amount of a transition metal, such as Ni and Co, it is possible to obtain dense sintered bodies. However, by using these added elements, there is the disadvantage of lowering thermal conductivity of the resulting alloy. Recently, by making the powder particles fine and maximizing the degree of mixing, the mechanical alloying methods, etc. have been recently applied in the industry. However, the above methods are susceptible to contamination by impurities and are not so easily adaptable to mass production. In particular, when making an alloy of 20 wt % or below of Cu, it is very difficult to obtain dense sintered bodies by an infiltration method or by a liquid-phase sintering.
Recently, Korean Patent No. 213,682 disclosed a technique of producing a dense W—Cu based alloy containing 10˜30 wt % of Cu by dissolving tungsten salt and copper salt in water, followed by removing salt during spray-drying and milling the composite oxides obtained above, and then reducing and compacting the composite powder, followed by sintering. By using this technique, the rearrangement of W particles within the aggregates of reduced powder in the green body is easy in the W—Cu based composite powder containing 20 wt % or less of Cu. However, this easiness maybe cause the formation of pores between the aggregates, and accordingly the sintered body cannot be fully densified.